The present invention relates generally to mechanisms for optimizing the operational efficiency of a turbocharger for an internal combustion engine, and more specifically to mechanisms for restricting engine exhaust flow supplied to and/or by a turbocharger turbine.
Exhaust gas recirculation (EGR) systems for internal combustion engines are known and are generally operable to selectively direct exhaust gas produced by the engine back into the fresh charge supplied to the air intake system for the purpose of controlling NOx emissions. In order to establish a positive flow of exhaust gas into the fresh air stream, the exhaust gas pressure must necessarily be greater than the intake air pressure. This requirement may be compromised in air handling systems including a turbocharger, and conventional turbocharger/EGR control systems accordingly include one or more mechanisms for managing turbocharger swallowing capacity in order to provide adequate back pressure to ensure positive EGR flow.
One known technique for ensuring positive EGR flow requires sizing the dimensions of the turbocharger turbine to provide a fixed geometry that is small enough to ensure positive EGR flow under all expected engine operating conditions. Alternatively, the turbocharger turbine may be configured to have a variable geometry, wherein the swallowing capacity of the turbine may be controlled by controlling the air flow geometry thereof. Alternatively still, the air handling system may include a wastegate operable to selectively direct exhaust gas around the turbocharger turbine in order to modulate the exhaust gas pressure.
While the foregoing techniques for ensuring positive EGR flow are generally operable to accomplish their particular goals, they have certain drawbacks associated therewith. For example, reducing the swallowing capacity of the turbocharger also has the undesirable effect of increasing the intake manifold pressure. If the turbine efficiency is higher than desired, the net result will be higher than desired turbocharger rotor speed, turbocharger outlet pressure, cylinder pressure and engine heat rejection. Moreover, fuel economy will suffer and soot loading of the oil will be worsened.
If the xe2x80x9capparentxe2x80x9d turbine efficiency can be managed without changing its physical air swallowing capacity, several operational advantages can be realized. For example, the EGR rate can then be increased so that injection timing can be advanced and fuel consumption thereby improved. Boost pressure can also be lowered, thereby increasing available engine power. Moreover, a larger geometry turbine can be used to allow for improvement in high speed power and fuel economy.
One known mechanism for managing apparent turbine efficiency is a variable flow rate exhaust throttle that typically includes a valve or similar mechanism that may be selectively controlled to correspondingly reduce or enlarge the effective flow area of the exhaust conduit. However, while such devices are generally operable to achieve their designed function, they are typically unreliable in operation. Moreover, such variable flow rate exhaust throttles undesirably add weight and significant cost to the air handling system. What is therefore needed is a simple, reliable and inexpensive mechanism for optimizing the apparent turbine efficiency to thereby improve engine output power and controllability.
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, a passive engine exhaust flow restriction arrangement comprises a turbocharger having a turbocharger turbine defining a turbine inlet operable to receive exhaust gas produced by an internal combustion engine and a turbine outlet operable to expel engine exhaust gas therefrom, a first engine exhaust conduit in fluid communication with the turbine inlet and defining a first cross sectional flow area therethrough, a second engine exhaust conduit in fluid communication with the turbine outlet and defining a second cross sectional flow area therethrough, and a passive flow restriction member disposed in line with either of the first and second engine exhaust conduits and defining a third fixed cross sectional flow area therethrough less than either of the first and second cross sectional flow areas.
In accordance with another aspect of the present invention, A passive engine exhaust flow restriction arrangement comprises a turbocharger having a turbocharger turbine defining a turbine inlet operable to receive exhaust gas produced by an internal combustion engine and a turbine outlet operable to expel engine exhaust gas therefrom, an exhaust conduit disposed in fluid communication an exhaust manifold of the engine and the turbine inlet, the exhaust conduit defining a first cross sectional flow area therethrough, and a passive flow restriction member disposed in line with the exhaust conduit and defining a second fixed cross sectional flow area therethrough less than the first cross sectional flow area.
In accordance with yet another aspect of the present invention, a passive engine exhaust flow restriction arrangement comprises a turbocharger having a turbocharger turbine defining a turbine inlet operable to receive exhaust gas produced by an internal combustion engine and a turbine outlet operable to expel engine exhaust gas therefrom, an exhaust conduit disposed in fluid communication between the turbine outlet and ambient, the exhaust conduit defining a first cross sectional flow area therethrough, and a passive flow restriction member disposed in line with the exhaust conduit and defining a second fixed cross sectional flow area therethrough less than the first cross sectional flow area.
One object of the present invention is to provide a passive engine exhaust flow restriction arrangement defining a fixed cross sectional flow area therethrough.
Another object of the present invention is to size such an exhaust flow restriction arrangement to optimize turbocharger turbine efficiency.
Yet another object of the present invention is to size such an exhaust flow restriction arrangement to optimize engine fuel economy.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiment.